In the world of manufacturing, integrated circuit wafers having nanometric features provide a profound challenge to the makers of equipment for inspecting the wafers for defects, and analyzing any defects found. Among devices that must evolve to meet the challenge are defect analyzers, devices for excising and preparing lamella from an IC die for imaging by a scanning transmission electron microscope (STEM) or a transmission electron microscope (TEM), referred to below as “TEM prep devices,” and critical dimension metrology STEM and TEM devices.
A defect analyzer is a machine that examines an etched semiconductor wafer, to find and analyze any defects in the wafer fabrication. One type of defect analyzer includes both a scanning electron microscope for surface inspection, and a focused ion beam (FIB) for micro-machining into the wafer to permit inspection of otherwise hidden surfaces. Many operations of a defect analyzer, similar to other machines, may be performed entirely automatically. For example, determining if a surface pattern sufficiently matches a predetermined template typically requires no human manual assistance. Other operations, such as further milling address instances in which there is not a sufficient match to wafer specifications, do require manual assistance.
TEM prep devices require cutting into the die with an FIB. It is also sometimes necessary to remove material from the lamella being excised (through micro-machining), thereby thinning the lamella to the point that the electron beam of a TEM or STEM can travel through it. Although a fair amount of thinning can be done automatically, determining when to stop may require human judgment. For example, if a lamella must be 80 nm thick to contain the feature of interest, an automated process may stop thinning at a safe 150 nm thickness. But after that point it may be necessary to have a human operator view the operation, to determine at what point the feature has been revealed, and the process can be stopped.
A critical metrology TEM or STEM is a device that is used to measure features of a die (typically excised on a lamella), to verify correct dimensionality. Although much of this measurement can be done automatically, in some instances human judgment is necessary to properly focus the device, or to determine the end points of a feature, where the boundaries are not clear.
For all of the above described devices, there may be instances in which the device automatically recognizes that human assistance is required. This type of human assist task would be impossible to predict in advance.
In one currently available device it is possible to schedule automatically performed tasks and manual assistance tasks. But the scheduling is not dynamic, so that when the schedule reaches a point where a task requiring manual assistance is to be performed, the machine finishes the last fully automatic task and stops performance until a human operator arrives to perform the manual assistance task. Likewise, when a human operator must leave before he is finished with a manual assistance task, there is no way to cause the machine to resume performing the fully automated tasks.
Because defect analyzers typically work on wafers that are loaded in sequence, there is generally a virtually infinite amount of work to be done on the train of wafers. Also, a wafer already treated by the defect analyzer can be reloaded into the machine later, for further treatment. Accordingly, even a manual task scheduled as the last job to be performed on a particular wafer can nevertheless cause a needless interruption in machine function, as it prevents the loading of a subsequent wafer until the manual assistance task is completed.